The present invention relates generally to a cover for enclosing a battery cell container made from a thermoplastic material, and in particular, to a cover which is capable of being bonded to the horizontal top edge of the container by radiant heating.
Ultrasonic sealing and butt-sealing with heat reflectors are the principal means used to mutually seal cell covers and cell containers apart from the more traditional gluing methods. However, the heat required to melt the edges of the cover and the container can also be applied to the surfaces to be joined as radiant heat, for example, by means of a hot wire. In all cases, a complete and reliable seal of the cell container, one which can also withstand extreme temperature variations and vibrations, is the desirable goal.
Container structures with meshing tongues and recesses are less favorable for ultrasonic bonding, because such structures tend to reduce the penetration of the ultrasound. In the case of butt-sealing with heat reflectors, the heat reflector must be precisely adapted to the contour of the edges of the container to which the cover is to be bonded, and must at least have openings for the cell poles which are to project from the inside of the container, above the plane of sealing.
In a battery container/cover sealing system according to EP No. 28 116, which is based on the principle of butt-sealing with heat reflectors, an otherwise one-piece heat reflector is subdivided into four heating elements which are moved from opposing positions to the long and broad sides of the container so as to form a heating ring only in a working position in which the front edges of the heating elements reach between the edge of the container and the edge of the cover. A narrow vertical gap into which fused material can escape from the actual horizontal sealing zone, so as to form an additional sealing zone, is developed between a skirt depending from the cover and the inner edge of the container by providing the underside of the cover with guide pins for proper positioning of the cover with respect to the container. To this end, the skirt connects the pins with one another, while being recessed somewhat behind the plane of the pins. However, in automating this method of assembly, extraordinary machinery and control systems are required. Moreover, such a method of assembly is only suitable for thick-walled containers.
Thus, it is the primary object of the present invention to provide a cover which is designed for use in the thermal bonding of covers to thin-walled containers by means of less expensive hot wires or heater bands, yet which is favorable to the efficiency of the bonding and the resulting tightness of the bond.